- Internal Working Model
- A mental framework — formed through early attachment experiences — representing the self as more or less worthy of care, and others as more or less reliably available. These models guide expectations and behaviours in relationships throughout life.
- Monotropy
- Bowlby's proposal that infants form a primary attachment bond with one particular figure (usually the mother) that is qualitatively different from all others. Subsequent research has questioned strict monotropy — children form multiple attachment hierarchies.
- Critical period for attachment
- Bowlby proposed that if an infant does not form a primary attachment before approximately 2.5 years, the capacity for normal emotional development would be permanently impaired — the maternal deprivation hypothesis. Later research has refined this to a sensitive rather than strictly critical period. Harlow's rhesus monkey isolation studies provided the most direct experimental evidence for this sensitive period.
- Sensitive responsiveness
- Ainsworth identified maternal sensitivity — accurately perceiving and promptly, appropriately responding to infant signals — as the key predictor of secure attachment. Hundreds of subsequent studies have broadly supported this relationship.
- Strange Situation Procedure
- A structured observational method in which a toddler (aged 12–18 months) experiences eight brief episodes involving separation from and reunion with the caregiver, and encounters with a stranger. The child's reunion behaviour is coded to determine attachment classification.
- Separation protest
- The distress shown by infants (typically peaking at 12–18 months) when separated from their primary caregiver. Its presence reflects an established attachment bond; its absence in young infants may indicate the bond has not yet formed.
- Adult Attachment Interview (AAI)
- A structured clinical interview developed by Mary Main that assesses how adults represent and make sense of their own childhood attachment experiences. Adults are classified as Autonomous, Dismissing, Preoccupied, or Unresolved — categories that predict the attachment security of their own children with approximately 75% accuracy, one of the most robust intergenerational findings in developmental psychology.
- Earned security
- Adults who had difficult early attachment histories but have developed a coherent, autonomous understanding of those experiences — typically through later positive relationships, therapy, or both. Earned-secure adults show similar parenting outcomes to continuously-secure adults, demonstrating that early attachment is influential but not deterministic.
- Validity and critiques of attachment theory
- Attachment theory has attracted several critiques. Cross-cultural researchers note that the Strange Situation may disadvantage children from cultures where brief separations are unusual. The stability of attachment across development is more modest than Bowlby predicted. Behavioural geneticists have highlighted the role of heritable temperament in shaping apparent attachment behaviours. Despite these challenges, attachment theory remains one of the most empirically supported frameworks in developmental psychology, with decades of longitudinal and cross-cultural evidence.
- Attachment across cultures
- Cross-cultural research using the Strange Situation finds secure attachment to be the most common pattern globally, but rates of insecure subtypes vary. German childrearing norms, for example, deliberately foster independence, producing higher rates of avoidant classification than US samples.